The present invention relates to a method of manufacturing a liquid crystal display unit. Specifically, it relates to a method for connecting a first circuit board on which a driver IC is mounted to a second board on which an LCD is mounted.
There have heretofore been known liquid crystal display units comprising a printed-circuit board with a driver IC mounted thereon and a second board on which the signal wires of a liquid crystal display device are mounted. The printed-circuit board is connected to the signal wires of the second board by a hot-melt connector with an electrically conductive material mixed therein. More specifically, the printed-circuit board and the second board supporting the liquid crystal display device (hereinafter referred to as the "panel board") are electrically connected to each other by positioning the hot-melt connector between the printed-circuit board and the panel board, and then heating the hot-melt connector through the printed-circuit board to melt the hot-melt connector. However, heating the hot-melt connector through the printed-circuit board has been disadvantageous in that various conditions such as the time and temperature at which the hot-melt connector is heated vary depending on the thickness, thermal conductivity, and other properties of the printed-circuit board, and that the wiring pattern on the printed-circuit board is generally made of a material which is a good heat conductor that will cause an undesirable temperature rise in surrounding parts. To avoid these shortcomings, it has been practiced to connect the printed-circuit board and the panel board with a bridge-like conductive connector through the hot-melt connector. With this method, however, the bridge connector adds to the cost of the liquid crystal display unit, and the efficiency of assembling the parts together is low since two connections have to be made, one to the printed-circuit board and another to the panel board. Another problem with this method is that the liquid crystal display unit is large in size because the components are connected in a planar configuration.
As disclosed in Japanese Laid-Open Patent Publication No. 58-105280, it is known to employ a heat-sealing connector in a dot-matrix liquid crystal display unit for reliably and easily connecting a liquid crystal display panel board having filamentary electrodes and a printed-circuit board. The heat-sealing connector comprises, for example, an insulating board and a hot-melt electrically conductive adhesive layer disposed on the insulating board. The heat-sealing connector is thermally fused and joined to the panel board at a high tempeature. However, inasmuch as the panel board has a limited heat-resistant capability, there is a limitation on the temperature to which the heat-sealing connector can be heated by a heating head, and the panel board tends to be deformed by the heat applied by the heating head, with the result that transparent electrodes on the panel board may be broken. Where the panel board is in the form of a glass sheet, it is necessary to provide a separate film-like connector as the heating time is increased due to the thickness of the glass sheet.